Wafer-level techniques may be used to produce multiple optical elements in parallel. Wafer-level techniques typically include forming a wafer including an array of optical elements, such as an array of lenses or an array of image sensors. The wafer is singulated, or in other words, divided into a number of pieces, to separate the optical elements of the array. Alternately, two more or wafers of optical elements are joined together to form a bonded wafer assembly, and the bonded wafer assembly is subsequently singulated to yield a plurality of optical assemblies, where each optical assembly typically includes an optical element from each wafer.
Optical elements of a given array are typically designed to be identical. For example, lenses of an array of lenses on a wafer will typically be designed to have identical properties. However, there are usually variations among optical elements in an array due to manufacturing imperfections. Such variations may require that some optical element instances be rejected, thereby negatively impacting manufacturing yield.
For example, FIG. 1 cross-sectionally illustrates several lens modules 100 of an array (not shown) of lens modules formed using wafer-level techniques. In this document, a specific instance of an item may be referred to by use of a numeral in parentheses (e.g., lens module 100(1)) while numerals without parentheses refer to any such item (e.g., lens modules 100). Lens modules 100 are designed to have a flange focal length (FFL) 102 of nominal value 104, where FFL 102 of a given lens module 100 is a distance from a reference plane 106 of the lens module to a focal point 108 of the lens module. FFL 102, however, will often vary at least somewhat from nominal value 104, as illustrated in FIG. 1, due to manufacturing imperfections. For example, lens module 100(1) has a FFL 102(1) that is shorter than nominal value 104, lens module 100(2) has a FFL 102(2) that is longer than nominal value 104, and lens module 100(3) has a FFL 102(3) that is equal to nominal value 104.
FIG. 2 cross-sectionally illustrates three optical assemblies 200 formed by joining lens modules 100 of FIG. 1 with respective image sensors 202 using transparent glue 204. Optical assemblies 200 are designed to generate an in-focus image when lens modules 100 have FFLs 102 equal to nominal value 104. Specifically, when FFL 102 of a given lens module 200 is equal to nominal value 104, the focal point 108 of the lens module will be aligned with an image plane 206 of its respective image sensor 102. Accordingly, optical assembly 200(3) will generate an in-focus image because its FFL 102(3) is equal to nominal value 104. Optical assemblies 200(1) and 200(2), in contrast, will not generate in-focus images because their respective FFLs 102(1) and 102(2) are significantly different from nominal value 104. Consequentially, optical assemblies 200(1) and 200(2) may not meet performance objectives and may therefore need to be rejected.